Integrated circuit (IC) chips are becoming more complex with increased circuit density and higher input/output (I/O) counts. In order to accommodate these IC chips, different types of IC packages have been developed, such as tape ball grid array (TBGA) packages, chip scale packages and flip chip packages. Of these different types of IC packages, TBGA packages have become popular due to their low cost and ease of manufacture.
A conventional TBGA package of interest comprises a tape substrate, an IC chip, and a conductive stiffener. The tape substrate includes at least one dielectric layer and one or more patterned metal layers. The patterned metal layers are typically used for signal transmission and AC signal ground connection. The patterned metal layers are electrically connected to the IC chip via wirebonds. In order to physically and electrically connect the TBGA package to a printed circuit board (PCB), the TBGA package utilizes a number of solder balls that are selectively connected to the patterned layers of the tape substrate. These solder balls are used to attach the TBGA package directly to a PCB or indirectly to the PCB via a socket, and to electrically connect the patterned metal layers of the tape substrate (and thus, the IC chip) to the circuitry on the PCB. The IC chip and the tape substrate are attached to the conductive stiffener, which provides structural support and electrical connection. The conductive stiffener is typically AC signal grounded or floated.
When the conductive stiffener of the TBGA package is AC signal grounded, the conductive stiffener generates electromagnetic signal into the surrounding environment, and thus, creates electromagnetic interference (EMI) to other electrical components near the TBGA package. In addition, the TBGA package is itself susceptible to EMI caused by electromagnetic field from the surrounding environment.
One technique to protect the TBGA package from EMI is to connect the conductive stiffener to AC ground, rather than to AC signal ground, so that the conductive stiffener can be used as an EMI shield. The two current methods to connect the conductive stiffener of a TBGA package to AC ground are (1) electrically connecting the conductive stiffener to the IC chip using first wirebonds and electrically connecting the IC chip to a patterned metal layer of the tape substrate using second wirebonds such that the conductive stiffener is electrically connected to the solder balls designated to be connected to AC ground via the first wirebonds, the IC chip, the second wirebonds and the patterned metal layer, and (2) electrically connecting the AC ground-designated solder balls directly to the conductive stiffener using apertures through the tape substrate.
A concern with the first method to connect the conductive stiffener to AC ground is that the method requires a significant amount of pad space on the IC chip and numerous wirebonds between the IC chip and the tape substrate. Another concern with the first method is that long electrical paths are created between the conductive stiffener to the AC ground-designated solder balls since each signal path includes one of the first wirebonds and one of the second wirebonds.
A concern with the second method to connect the conductive stiffener to AC ground is that this method requires a special packaging process to attach the AC ground-designated solder balls to the conductive stiffener using the apertures through the tape substrate.
Consequently, there is a need for a TBGA package with EMI protection and method for fabricating the TBGA package that alleviates some or all of the above-described concerns.